At present, an active matrix organic light emitting diode (AMOLED) panel uses a thin film transistor (TFT) to drive an organic light emitting diode (OLED) to emit light.
An AMOLED pixel circuit adopts generally a 2T1C circuit comprising two TFTs and one capacitor. In this 2T1C circuit, the current IOLED flowing through OLED is calculated by the equation of:
      I    OLED    =            1      2        ⁢                  μ        n            ·      Cox      ·              W        L            ·                        (                      Vdata            -            Voled            -            Vthn                    )                2            where μn, is a carrier mobility, Cox is a gate oxide layer capacitor, W/L is a width to length ratio of the transistor, Vdata is a data voltage, Voted is an operating voltage of OLED shared by all the pixel units, and Vthn is a threshold voltage of the transistor. Vthn is a positive value for an enhancement type TFT, while Vthn is a negative value for a depletion type TFT.
However, due to limitation of crystallization process and manufacturing level, non-uniformity always occurs in electrical parameters such as threshold voltage, mobility and so on of the TFT switching circuit manufactured on a large-area glass substrate, such that threshold voltage offset of respective TFTs is inconsistent. It can be known from the above equation that currents flowing through different OLEDs have a difference if Vthn among different pixel units is different. If Vthn of pixels drifts with the time, this may result in that currents flowing through successively the same OLED are different, thereby causing image sticking. Furthermore, because non-uniformity of the OLED devices causes the operating voltages of OLED to be different, it may also result in current difference, thereby causing difference in display brightness of AMOLED.